A 15% drop in viewers is on par for most shows in their second week, and the overall numbers for "Under the Dome" are still very strong. It easily finished first in the key 18-49 and 25-54 demographics.

The audience for "Under the Dome" will likely grow when digital video recording numbers are factored in. More than 3 million people recorded the first episode of "Under the Dome" and watched it within three days of its June 24 debut. CBS also repeated the premiere on Sunday, when it drew 5.1 million viewers. CBS plans to repeat Episode 2 this coming Sunday.

Though the first episode of "Under the Dome" got solid reviews, the second episode was not as well received. Variety critic Brian Lowry said the episode planted "seeds of doubt regarding whether 'Under the Dome' really has legs."

The industry is following "Under the Dome" closely. If it can hold its audience, it may lead the broadcast networks to make a bigger push into scripted big-budget programming for the summer.

Elsewhere, NBC's new drama "Siberia" struggled to get out of the gate, averaging just 3.2 million viewers. ABC's"Mistresses" averaged almost 4 million viewers.